1. Field of the Invention
The present invention relates generally to a method for allocating a common channel in a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to an apparatus and method for allocating a common channel in the case that a serving radio network controller (SRNC) is different from a drift radio network controller (DRNC).
2. Description of the Related Art
With the rapid development of the mobile communication industry, a future mobile communication system will provide not only a voice (circuit) service but also advanced services such as a data service and an image service. Generally, the future mobile communication system employs a CDMA (Code Division Multiple Access) system. The CDMA system is classified into a synchronous system and an asynchronous system. The synchronous system is chiefly adopted in United States, while the asynchronous system is mainly adopted in Europe and Japan. However, the standardization work on the future mobile communication system is being separately carried out for the synchronous system and the asynchronous system. The European future mobile communication system is called “UMTS (Universal Mobile Telecommunication System)”.
The standardization provides various specifications for the data service and the images service as well as the voice service, required in the future mobile communication system, and particularly, for channel allocation.
A UMTS W-CDMA (Wideband Code Division Multiple Access) communication system, the European future mobile communication system, uses a random access channel (RACH) and a common packet channel (CPCH) as a reverse common channel, and uses a forward access channel (FACH) as a forward common channel.
Among the reverse common channels of the W-CDMA communication system, the RACH can have characteristics dependent on a TTI (Transmit Time Interval) and a channel coding mode, and is mapped with a physical random access channel (PRACH) on a one-to-one basis. Further, the PRACH can have characteristics being dependent on available signatures and an access sub-channel. Therefore, the RACHs can be distinguished (identified) based on the TTI and the channel coding mode, while the PRACHs can be distinguished according to the number of available signatures and the access sub-channel. In addition, an available spreading factor (SF) can be also used in distinguishing the PRACHs.
As the RACHs and PRACHs have various characteristics, they can be used for different purposes according to their service types. In addition, information on the RACH/PRACH is broadcast by a Node B, and upon receiving the RACH/PRACH information, a UE can select which RACH/PRACH to use depending on the received RACH/PRACH information. Alternatively, the Node B can select the RACH/PRACH to be used by a specific UE based on a service to be used by the UE, and then inform the UE of the selected RACH/PRACH.
Like the RACH, the FACH and the CPCH also have different characteristics to provide different services, so that the UE can select proper FACH and CPCH according to the characteristics of the FACH and CPCH provided from the Node B. Alternatively, the Node B can determine the FACH and the CPCH to be used by the UE and then transmit information on the determined FACH and CPCH to the UE.
Meanwhile, common channels such as the RACH, the FACH and the CPCH are allocated to the UEs by a serving radio network controller (SRNC). The SRNC connected to a core network (CN) exchanges information on a service provided between the UE and the CN. The SRNC determines a channel to be allocated to the UE using the service information transmitted from the CN.
Shown in Tables 1A to 1C are RAB (Radio Access Bearer) parameters of a service information message used by the CN to inform the SRNC of the service information.
TABLE 1AIE type andSemanticsIE/Group NamePresenceRangereferencedescriptionRAB parameters>Traffic ClassMENUMERATEDDesc.: This(conversational,IE indicatesstreaming,the type ofinteractive,applicationbackground, . . . )for which theRadioAccessBearerservice isoptimised>RABMENUMERATEDDesc.: ThisAsymmetry(SymmetricIE indicatesIndicatorbidirectional,asymmetryAsymmetricor symmetryUnidirectionalof the RABdownlink,and trafficAsymmetricdirectionUnidirectionalUplink,Asymmetric Bi-directional, . . . )
TABLE 1B>DeliveryMENUMERATEDDesc.: This IE indicates that whether the RAB shall provideOrder(delivery orderin-sequence SDU delivery or notrequested,Usage: Delivery order requested: in sequencedelivery orderdelivery shall be guaranteed by UTRANnot requested)on all RAB SDUs Delivery order not requested:in sequence delivery is not required from UTRAN>MaximumMINTEGERDesc.: This IE indicates the maximum allowed SDU sizeSDU size(0.32768)The Unit is: bit. Usage: Conditional value: set tolargest RAB Subflow Combination compound SDU sizewhen present among the different RAB Subflow Combination>SDU parameters1 toSee belowDesc.: This IE contains the parameters characterizing<maxRABSubflows>the RAB SDUsUsage: Given per subflow with firstoccurrence corresponding to subflow#1 etc*>TransferC-iftrafficConv-INTEGERDesc.: This IE indicates the maximum delay forDelayStream(0.65535)95th percentile of the distribution of delay forall delivered SDUs during the lifetime of a RAB,where delay for an SDU is defined as the timefrom a request to transfer an SDU at one SAP to itsdelivery at the other SAP The unit is: millisecond.Usage:
TABLE 1C>TrafficC-iftraffic-INTEGER {spareDesc.: This IE specifiesHandlingInteractiv(0), highest (1),the relative importanceprioritylowest (14), nofor handling of all SDUspriority usedbelonging to the radio(15)) (0?5)access bearer comparedto the SDUs of otherbearersUsage:>Allocation/OSee belowDesc.: This IE specifiesRetentionthe relative importanceprioritycompared to other Radioaccess bearers forallocation and retentionof the Radio accessbearer.Usage:If this IE is not received,the request is regarded asit cannot trigger thepreemption process and itis vulnerable to thepreemption process.>SourceC-iftraffic-ENUMERATEDDesc.: ThisStatisticsConv-stream(speech,IE_specifiesdescriptorunknown, ?characteristics ofthe source ofsubmitted SDUsUsage:
The SRNC selects a dedicated channel (DCH) or a common channel using the RAB parameters shown in Tables 1A to 1C. If the common channel is selected, the SRNC can select the RACH or the CPCH in response to a service request. In addition, a maximum bit rate and a guaranteed bit rate are used in selecting a minimum SF and a channelization code to be used by the common channel. That is, the SF and the channelization code to be used by the common channel are determined depending on the maximum bit rate and the guaranteed bit rate. Here, the maximum bit rate and the guaranteed bit rate are bit rate information of the packet data.
In addition, a traffic handling priority and a transfer delay are selected based on the characteristics of the physical channel, i.e., based on the sub-channel and the number of signatures.
When the UE, with a channel allocated by the SRNC, performs a handover (or handoff), a DRNC, an RNC of a Node B newly accessed by the UE, and the SRNC may be changed. The SRNC and the DRNC are distinguished from the viewpoint of the UE. If the SRNC is connected to the UE not directly, but through the DRNC, then the SRNC cannot personally select a channel and allocate the selected channel to the UE.
The reasons that the SRNC cannot personally allocate a channel to the UE are as follows.
First, channels allocated to a cell in the DRNC are determined by the DRNC, because the SRNC does not have information on the allocated common channel in the DRNC. For this reason, the SRNC cannot determine a common channel allocated to the cell in the DRNC. Second, the DRNC or the CN does not have information on a service provided to the UE, so it is difficult to allocate a common channel to be used by the UE. Thus, conventionally, when the SRNC is connected to the UE through the DRNC, i.e., when the UE performs a handover, the UE cannot be allocated a common channel.